A variety of agents, including receptor agonists/antagonists, and synthetic and natural products,modulate ion channels and generation of second messengers, including cyclic nucleotides,inositol phosphates diacylglycerides, arachidonic acid prostaglandins, sphingosine, and phosphatidic acid. Calcium, sodium and potassium ions after translocation through ion channels or by transport proteins can release and transport processes, contractile proteins, cyclases, phosphodiesterases, protein kinases, phospholipases and ATPases. Modulatory interactions or "cross-talk" occurs both between the second messenger systems and the ion transport systems. The research of the past year concerned capacitative calcium entry through store-operated calcium (SOC) channels, effects of caffeine and analogs on GABA(A) receptor-channels and ryanodine-sensitive calcium-release channels, effects of riboflavin on adenylyl cyclase, and effects of various synthetic and natural products on sodium, potassium and nicotinic channels and muscarinic receptors. Loperamide, a potent blocker of maitotoxin-activated channels, selectively enhances elevation of intracellular calcium linked to influx of calcium through SOC channels, while having no effect on basal levels of calcium or on sphingosine-elicited increases in calcium. Loperamide reduces the efficacy of SOC channel blockers. Syntheses of analogs of loperamide to probe structure activity relationships are planned. A variety of evidence on activation, blockade and temperature-dependency suggests that there are subclasses of SOC channels even within a single cell type. The imidazoles, such as miconazole, were found to cause both release of calcium from IP(3)-sensitive pools and blockade of the SOC channels that open as the result of such release. Structure activity relationships are not the same for release from pools and blockade of SOC channels. Further analogs will be synthesized phenothiazines, such as trifluoperazine, and other tricyclics were found to cause little release, and to be effective blockers of SOC channels. Caffeine and analogs were found to inhibit binding of ligands to both benzodiazepine- and picrotoxinin-sites on GABA(A) receptor-channels. Effects on ion flux will be studied. Caffeine and analogs were discovered to have both stimulatory and inhibitory effects on binding of ryanodine to calcium-sensitive release channels. Certain analogs caused only inhibition, while others caused mainly stimulation. Effects on release of calcium from ryanodine-sensitive storage sites are under investigation. Riboflavin, a weak antagonist at A(1)-adenosine receptors, was found to cause both inhibition of turnover of guanyl nucleotides at G-proteins and an apparent direct inhibition of adenylate cyclase. A synthetic analogs of the alkaloid epibatidine were investigated as selective agonists at nicotinic receptors and have provided further insights into the nicotinic pharmacophore. Synthetic analogs of baogongteny A, a tropane alkaloid that were selective for the M(1)-muscarinic receptors or for the M(2)-receptors were discovered. One analog appears to have similar potency at nicotinic and muscarinic receptors. Behavioral effects, including analgesia, will be probed. A variety of alkaloids were studied as noncompetitive blockers of the major nicotinic receptor-channels, but all were nonselective or selective for the ganglionic class. Certain potent structures were identified. Investigation of structure activity relationships of the myotonic/cardiotonic alkaloids of the pumiliotoxin class at sodium and calcium channels has been restarted using sodium flux, calcium release and a new paradigm for batrachotoxin binding. There is markedly different structure activity relationships for activation of sodium flux as compared to blockade. Quaternary amines, imidazoles, peptides and various alkaloids are under study as blockers of potassium channels.